1. Field of the Invention
The present invention relates to a method for producing high quality activated carbon with a large surface area and a very low sulfur content.
2. Brief Description of the Prior Art
Activated carbon having a BET specific surface area in excess of 2000 m.sup.2 /g is useful for various purposes, such as fractionation of hydrocarbons, purification of industrial gases, anti-pollution devices, liquid-phase purification processes in food and chemical industries, water treatment, liquid-phase recovery and separation processes, catalysts and catalyst supports, and so on.
As a technology for producing such activated carbon having a large surface area, the following potassium hydroxide activation process has been proposed.
Japanese Patent Publication No. 61529/1987 describes a process for producing activated carbon with a BET specific surface area in excess of 2300 m.sup.2 /g, which starts with petroleum coke or a mixture thereof with coal as the carbonaceous material, and comprises blending this carbonaceous material with granular potassium hydroxide hydrate, dehydrating the blend in a preliminary calcining furnace at an elevated temperature of about 315.6.degree. C. (600.degree. F.) to 482.2.degree. C. (900.degree. F.) and activating the same in a calcining furnace at an elevated temperature of about 704.4.degree. C. (1300.degree. F.) to 982.2.degree. C. (1800.degree. F.).
In fact, the activated carbon obtained by the above process has a large BET surface area of 2300 m.sup.2 /g or more. However, our verification studies and analysis revealed that this activated carbon had a total sulfur content of about 0.3 weight percent and, when used as a catalyst support, presented the problem that the catalyst was poisoned.
The amount of sulfur contained in activated carbon can be decreased by washing the carbon with an acid, but the ultimate sulfur level after repeated acid washing is only about one-third of the initial total sulfur level at best. It is commercially impossible to reduce the total sulfur content to less than 0.01 weight percent (100 ppm). Furthermore, repeated acid washing means a high production cost and cannot be practiced commercially if only from this point of view.
It is, therefore, the object of the present invention to provide a commercially useful method for producing activated carbon having a large surface area and a very low sulfur content.